1. Field of the Invention
The present invention relates to a rapid thermal processing system and sulfidation method thereof, and more specifically, to a rapid thermal processing system utilizing a rapid thermal process to heat a sulfur in solid form and a selenium layer which are formed on a cover and a back electrode substrate respectively and opposite to each other and a sulfidation method thereof.
2. Description of the Prior Art
In general, there are three types of sulfidation methods of utilizing a rapid thermal process to form a CIGSS (copper indium gallium selenide sulfide) layer: utilizing H2S gas to react with a CIGS (copper indium gallium selenide) layer, directly heating a sulfur in solid form and a selenium layer with a CIG (copper indium gallium) stacked layer, and supplying sulfur steam to react with a CIGS layer.
The first sulfidation method involves utilizing a rapid thermal process to heat a back electrode substrate having a CIGS layer formed thereon to a specific temperature (e.g. greater than 500° C.) and then supply H2S. Accordingly, a substitution reaction may occur between H2S and the CIGS layer so as to form a CIGSS layer. The drawback of this method is that H2S is a harmful gas and time needed for the substitution reaction occurring between H2S and the CIGS layer is too long.
In the second sulfidation method, excessive diffusion of sulfur may occur since a sulfur in solid form could directly react with a CIG stacked layer to form a CIGSS layer. Thus, this method may cause a significant decrease of current and make the subsequent sulfidation reaction hard to control because the reaction rate of the sulfur in solid form and the CIG stacked layer is too fast.
In the third sulfidation method, sulfur steam may be attached to a precursor layer on a back electrode substrate so as to cause an uneven sulfidation problem if the sulfur steam is supplied in the initial stage of a rapid thermal process. If the sulfur steam is supplied during the rapid thermal process instead, the sulfur steam may react with the CIGS layer in different temperatures so as to influence the forming quality of the CIGSS layer. On the other hand, if the sulfur steam is supplied after the back electrode substrate is heated to a specific temperature (e.g. greater than 500° C.), it may further cause the problem that time needed for the substitution reaction occurring between the sulfur steam and the CIGS layer is too long.
In summary, each of the aforesaid sulfidation methods has its own drawback. Thus, how to reduce the process time of the sulfidation process and improve the sulfidation quality of the sulfidation process is an important issue of the solar industry.